Gunfire director



April 17, 1951 Filed Aug. 22, 1947 D. J. STEWART 2,549,030

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April 17, 1951 D. J. STEWART GUN FIRE DIRECTOR l1 Sheets-Sheet 11 Filed Aug. 22, 1947 Patented Apr. 17, 1951 UNITED STATES PATENT OF Fil-CE 2,549,030 GUNFIRE DIRECTOR Secretary of War Application August 22, 1947, Serial N0. .770,114

12 Claims.

This invention relates to an improvement in gun fire directors, and more-particularly, to directors intended for determining and controlling the fire of intermediate calibre guns against-moving targets, such as aircraft. In firing at rapidly moving targets, such as aircraft, the gun must be aimed so that its trajectorypasses through a point lying upon the forwardly-extended path-of the'target. The exact point is determined by the distance which the target travels along said path from the time the gun is fired until the projectile reaches the point of impact. In other words, the angle by which the gun must lead the target is that angle subtended at the gun,'by a distance extended forwardly along the target path, equal to the product of speed of target (assumed to remain constant), and the time of flight of the projectile. The lead angle thus obviously depends on target speed, target course and range, in addition to numerous other well-known variables such as windage and type of ammunition. Of course, .superelevation must be added to the vertical component of leadto determine thecorrect angle of gun elevation.

The purpose of .all directors is to determine, inter alia, the aforementioned lead angle or, rather, its vertical and horizontal components andto algebraically add other component angles so that the gun, when aimed in accordance with the outputs of angular values of the director, will be'continuouslyproperly aimedto hit the target,

Such directors .are well known; and while the invention may be used in connection with numerous kinds and types of directors, it will be described in connection with the Armys types M5, M5A1, or M6. In a typical installation, the director/and gun are electrically connected so that after initial adjustment, the director as it is moved to maintain its; line of sight upon the target, supplies electricalimpulses to the gun in ac- :ordance with the computed lead angles. These .mpulses are utilized to control power drives at ;he gun which automatically ,move the ,gun in :rain and elevation to continuously maintain it Jroperly'laid. Since range is an indispensable in- Jut value, it must be estimated or determined. Previously, it was customary ior the range to be manually set into the instrument on the basis if estimation, or the reading of a separate range inder. In all cases the initial range setting is :ubsequently modified :by spotters corrections, lased ,upon observation of tracers. Because of he extremely high speeds of ;modern aircraft ind {the errors inherent in unaided observation ltlongranges-the prior art procedures have beome obsolescent even for ammunition using roximity .or variable time fuses.

Accordingly, it is ,an:.object of my invention to 2 provide a director having a range finder thereon and trainableas a unit therewith.

Another object is to provide the combination of a director and coupled range finder wherein manual adjustments of the range finder to focus the same upon a target, automatically introduces the range of the target into the director.

Another object is to provide a range finderin which the altitude, rather than the range, is set, the instrument automatically operating to combine altitude and angle of elevation of the line of igh t d rmine. ran e.

A still further object is to provide a servo mechanism automatically controlledby the range finder for setting range into the director.

A further object is to provide a novel range finder, preferably of the full field superposed image type and having two separate oculars whereby simultaneous observations may be made by the operator and a spotter or tracer observer.

Pursuant to the immediately foregoing object, anauxiliary object is to provide a range finder having a novel mount for one entrancereflector whereby said reflector may be independently ad justed about each of two mutually normal axes to properly calibrate and adjust the instrument.

A still further object is to provide a reflector mount for a range finder in which adjustment of the reflector is abouttwo mutually normal concurrent axes, one-parallel with the line of sight determined thereby and the other normal to said line of sight-and the axis of the instrument.

A further object is to provide a combined gunfire director-and a rangefinder wherein the range set into the director may be manually modified on the basis of tracer observations made through the range finder.

A still further object is toprovide novel potential-balancing and =follow-up control circuits wherebythe range setting offthe director is ef fec'ted in a smooth and continuous manner and with substantially instantaneous response.

Still another object is the provision of a novel method of determining-range and altitude of an object.

Qther objec s-a d ad a e .of t nvention willbecome' apparent as the description proceeds.

Inthe drawings:

Figure 1 is a perspective View looking toward the right rear corner, of ;.a director -.and range finder embodying the invention and showing, inter alia, the azimuth trackers telescope and andhe l. the aneez ndeli a -serv nrohb x, n. -,,-rang "fi der control box,

Figure :2 is .a perspective diagrammatic -.-view of the optical .elements .-of .the range finder, zt'he range cam and disc unit, together with the me 3 chanical connection between the cam and the adjustable reflector,

Figure 3 is a longitudinal section of the right end of the range finder tube taken in a plane par allel to a plane through the lines of sight and showing in plan the adjacent mirror, its pivotal mounting and the means for effecting adjustment thereof about a first axis normal to the central axis of the range finder tube and the line of sight, and a second axis parallel with the line of sight. 7

Figure 4 is a sectional detail view taken upon a plane indicated by the line l4, Figure 5, and showing details of the mirror and its mounting,

Figure 5 is a sectional detail view taken upon a plane indicated generally by the line 55,

Figure 4, showing the mechanism for effecting the height adjustment of the adjacent mirror,

Figure 6 is an end elevation of the mounting frame for the mirror,

Figure 7 is a perspective View of an alternative form of mirror-mounting and adjusting mechanism,

Figure 8 is a detail perspective view of the mounting sector and gear of the unit shown in Figure '7,

Figure 9 is a vertical axial section of the unit of Figure 7 taken in a plane through the line of sight.

Figure 10 is a perspective view of that'portion of the altitude converter mounted upon the range finder and having its cover removed to show details of construction,

Figure 11 is a schematic detail View showing the mechanical coupling between the range cam and the slider of the slant range potentiometer,

Figure 12 is a section through the axis of the slant range potentiometer of Figure 10, showing the final portion of the power drive thereto,

Figure 13 is a rear perspective, with cover removed, of the range servo and control mechanism carried on the rear wall of the director,

Figure 14 is a detail axial section of the range adjustment potentiometer appearing in Figure 13,

Figure 15 is a section on a plane indicated by the'line 15- I 5, Figure 14, showing the means for urging the spotters range adjustment handle 7 and potentiometer handle, to central or initial position,

Figure 16 is a horizontal section through the pivot axis of the range servo potentiometer of Figure 13, showing the details of the driving connection between the potentiometer and the range servomotor,

Figure 17 is a detail perspective view of the right hand end of the director sight shaft showing the azimuth telescope and the mechanical connection between the sight shaft and the sine E potentiometer,

Figure 18 is an axial section showing in detail the friction anti-hunting coupling between the shaft of the range finder motor and its flywheel,

Figure 19 is a simplified wiring diagram of the several potentiometers, and their connections to each other and the. servo motors through the amplifier,

Figure 20 is a complete wiring diagram of the altitude converter parts mounted upon the range finder,

Figure 21 is a complete wiring diagram of the range servo mechanism on the director and its connections to the altitude converter parts on the. range finder and the amplifier in the director,

Figure 22 is a complete wiring diagram of the amplifier and its connections with the range servo and altitude converter,

Figure 23 is a view showing the field of view of the range finder operator when the range finder is properly adjusted and focused upon a target,

Figure 24 is the view corresponding to Figure 23. as seen by the tracer observer in his eyepiece on the range finder, and

Figures 25 to 30, inclusive, are typical views as seen by the tracer observer in his field of view during combat.

The director in general In order to fully and adequately disclose the invention, it has been shown, merely by way of example, as a part of an M5 Army director. This director is generally identified by the numeral l and is supported by a tripod consisting of legs 3 surmounted by a head 2. Three leveling knobs G, are journaled on head 2 at the ends of equal, and equally spaced radii about the central axis of the head. Each knob controls the vertical adjustment of a respective, upwardly-projecting plunger, not shown. Each plunger fits a corresponding socket in the base of the director, whereby the director I may be leveled in a wellknown manner. The main portion of the director including casing 5, is journaled for movement about a normally vertical axis relatively to the aforementioned base. Azimuth handwheel Bis journaled in casing 5 and is geared to base so that rotation of the handwheel effects movement in azimuth of the casing and all parts carried thereby.

A sight shaft '1, Figure 17, is journaled at its ends in casing 5, as by means of bearings, one of which is identified at 8. The shaft is normally horizontal. An azimuth elbow telescope 9 having an ocular Ill is adapted to be fixed to the right projecting end of shaft 'i and has a reticle in the field. of View comprising vertical and horizontal intersecting lines. This reticle may be illuminated by a lamp in housing ll, supplied by current over a cable I2. The tripod legs 3 are of a height such that ocular It is substantially at eye level; In operation, the azimuth tracker or trainer stands with an eye at ocular l0 and by manipulation of handwheel 6, trains the entire casing 5 about the vertical axis to keep the vertical reticle line in his telescope on the target.

A handwheel 13, Figure 1, is journaled on cas Y ing 5 and geared by means, not shown, so that rotation thereof, moves shaft 1 in its bearings 8 and changes the elevation angle of the line of sight. The lines of sight of the two telescopes are, of course, parallel. Thus, in operation, the elevation tracker, or pointer, looks into his telescope and manipulates his handwheel l3 to rotate shaft 1 and keep the horizontal cross hair of his telescope on the target. The director base rests on. the upwardly-projecting ends of plungers controlled by knobs 4 and is manually positioned on the tripod and removed therefrom, by front and rear porter bars each passing through an aperture I4 in the ends of carrying brackets 15. The front pair of brackets are fixed to ashaft l6 journaled on the front lower surface of casing 5. Likewise, the rear pair of brackets are fixed to a shaft ll journaled on the rear lower surface of the casing. Electrical con-r nections to and from the director are made by a multi-pole D-plug inserta-ble upwardly into a receptacle in the lower portion of the instrument.

While it is one function of the present invention to automatically introduce range into the director under-control of the range finder, as will be subsequently explained, range may be manually introduced by hand wheel I8, as in prior Army models. Whether range is introduced manually or automatically, the instantaneous range being set into the instrument, is indicated by a dial [9 rotatable within an opening 20 in the rear wall of casing 5. Additional features common to the aforementioned models are identified as coarse firing azimuth dial 2|, 'fine azimuth firing dial 22, constant speed gear observation window 23, zero deflection mark observation window 24, rate setting clutch control 25 and switch 26. Numerals 2'! identify spring buifers projecting from the lower surface of casing 5 and by which the entire instrument is resiliently supported and protected against shock when in its packing case.

The director, as thus briefly described is standard Army equipment, and, per se, forms no :part of my-invention. The director is, in effect, a

:omputer wherein certain input values such as present azimuth and azimuth rate of the target, present elevation and elevation rate, and range )f target, are introduced. The director takes shese values, properly combines them, and from ihem computes and supplies output values in- :luding a value of quadrant angle of gun eleva- Zion and train angle measured from a predeternined horizontal base line, through whioh'the gun must be elevated and trained in order to hit Jhe target being tracked. These values'may be ;ransmitted to'thegun by conventional electric :elemetric connections where they are utilized either to directly control the gun through fol- .ow-up and servo-motor controls, or used to effect ndications for manually actuated folloW-theaointer control. The directors, as just described,

require a crew of three men, namely an azimuth n'acker, an elevation tracker and a range setter. In these prior instruments, range may be ob- ;ained from a separate range finder or the range :etter may estimate the initial range and make iubsequent corrections on the basis of the ob- ;erved tracer paths.

The range finder in general ull field, superposed image type of instrument mounted in anti-friction bearings for pivotal movement about its longitudinal axis in brackets 8 and 29. These brackets are bolted to the ight and left sides, respectively, of casing 5, at he rear upper corners thereof. The finder tube 0 is thus journaled for rotation about its longiudinal axis, which axis is fixed parallel with haft I. The lines of sight of the elevation and .zimuth telescopes must be kept parallel with hose of the range finder. This function may be lerformed by any suitable mechanism, connectng shaft '1 and tube 39 for'equal pivotal movement insynchronism. One satisfactory way is 'ceive a frame 49.

by the use of a parallelogram linkage comprising parallel lever arms of equal effective length connected to shaft 1 and tube 30, respectively, and

having their radially outer ends connected by a link equal in effective length, to the distance between the axes of the shaft 7 and tube 30, as will be understood by those skilled in the art. A clamp such as 53, Figures 1 and 10, may be used to provide an open sight on the range finder, the line of sight being determined by a rear notch 53a and a forward point 531). The line so determined is, of course, parallel to that of the range finder, whereby the target may be picked up without loss of time.

The entrance reflector mounts of the range finder The optical elements of the range finder are shown at Figure 2, where 3| identifies the left entrance total reflector .or mirror, mounted in a frame 32 and provided with aligned trunnions 35 and 3-6 for movement in casing 30 about the axis defined by said trunnions. This axis lies in the reflecting surface of the mirror and is normal to the longitudinal axis of the finder. At its inner side,mirror 3| carries a small prismshaped element 33 having a plane silvered reflecting surface generally normal to the longitudinal axis 3% of the tube or casing 30. Frame 32 has a lever 3! connected thereto. This lever extends axially along the casing where its right end is held in contact with an equi-crescent cam 38 by a leaf spring 39 fixed at one end to a portion 49 of the range finder frame.

Cam '38 is fixed. to a shaft journaledin the casing on an'axis normal both to axis 30b and the line of sight to the target. This shaft also has fixed thereto a transparent disc 42 having scribed thereon a spiral range line 43, and a range scale 44 shown at Figure 23. The reflections of this range line and scale appear within masked outlines 45 of reticle disc 46 (Fig. 23) where the instrument is shown properly adjusted for range, with image 43 of line 43 centeredbetween two parallel fiducial lines etched on reticle 46. The range is indicated as 1250 yards in the figure.

The inner reflector 48 is a partially silvered mirror mounted, by means now to be described, for movement about two mutually normal axes, namely, a first axis normal to the axis 302) of the tube 30 and a second axis normal to the line of sight to the target. Referring to Figures 3 to 6, inclusive, it will be noted that the ocular end of casing 39, is rabbett-ed as at 36a to re- This frame may be held in place by a flanged end cap 59 secured to the end of tube 3!! by screws 5!. Cap 5a is formed to support the'range finding ocular, generally identified'bynumeral 52. See also Figure 10. The ocular may be a standard Erfle so that it is deemed sufilcient merely to identify, on Figure 2, first and second eye lens 54 and. 55, and field lens 56. The cap also has bearing support apertures for a pair of adjustment knobs 5'! and 58 which are operable by the range finder operator, to adjust mirror 88 about its two axes, as subsequently explained. Sets of slip friction discs59 and 60 connect each knob with its driven parts and act to prevent damage to those parts which might otherwise be effected by excessive torques applied to the knobs, as for example, when the parts have reached their limits of move ment.

Framed!) is formed'to provide a pair of-arms 6| and 62, Figure rprojecting axiallyof tube 7 left side thereof.

. v 7 39 on the side adjacent mirror 48 and. at the lower side of said axis. These arms have aligned apertures at their ends defining an axis parallel to the adjacent line of sight 66 of the range finder. The apertures are threaded to receive bearing screws 63 and 64, socketed at their inner or confronting ends to journal therebetween, a support 65 for pivotal movement about said axis. Mounting is conveniently and accurately effected by a pair of steel balls, each seated in conical or hemispherical depressions in lugs 61 and 68, Figure 5, and in the aforesaidbearing pins. At its top portion, on the side of axis 39!) of tube 39 remote from arms 6| and 62, support 65 has an aperture in which a contact pin 69 is threaded, Figure 5. This pin is adapted to be locked in adjusted position by a set screw I9 and extends generally parallel with axis 39b. Frame 49 has a splined aperture in alignment with pin 69 in which fits an internally threaded and correspondingly splined. bushing H. The bushing is shouldered at its inner end and is held firmly in position in frame 49 by a nut 12 threaded upon its outer end. The inner or headed end of bushing H is recessed to fixedly receive 'a small plate 15 having a squared central opening in alignment with pin 69. A sleeve 13 is externally threaded to engage the internal threads of bushing H, and internally threaded to receive a threaded contact plunger 14. This plunger has a squared reduced forward end 14a fitting the squared aperture in plate 15. The threads between bushing TI and sleeve 13 are of a different pitch than those between sleeve 13 and plunger 14 so that, as the sleeve is turned, plunger 14 is advanced or retracted in pure translation to effect a very fine pivotal movement of support 65 about its pivot axis, previously described. From Figure 3, it will be noted that a pair of pins 16 and 11 are fixed in frame 49 and project loosely through respective holes 18 and 19 in support 95. These pins have headed ends and light coil springs 89 and SI surround the respective pins and exert their thrusts between the heads and support 65, to urge the pin 69 into contact with the end of plunger 14.

As best shown at Figure 5, sleeve 13 has an enlarged and apertured end which receives with a smooth fit the adjacent end of a drive shaft 82 having its enlarged ends formed as ellipsoids of revolution. A connecting pin 83 extends through a transverse hole in the enlarged end of the shaft and its projecting ends fit within axially-extending slots in sleeve 13, as clearly shown upon Figure 3. A ring 84 snaps into a circumferential groove in the end of sleeve l3 and holds the end of the shaft in place[ The other end of shaft 82 projects within and is similarly coupled with a sleeve 85 attached to knob 51. Thus, for each rotation of knob 51 a fine pivotal adjustment of support 65 and the parts carried thereby, is effected, the movement per rotation depending upon the difierence in pitch of the two screw threads. It Will be noted that the pivot axis defined by pins 53 and 64 is, at all times, very nearly coplanar with the point of contact of pin 69 and plunger 14, in a plane normal to the tube axis 39?).

Referring to Figures and 6, support 65 has a pair of vertically spaced lugs 85 and 81 at the These lugs have aligned holes, threaded to receive bearing pins 88 and 89 which may be identical with pins 63 and 54. A bracket99 has parallel lugs 99a and 99b adapt ed to extend between lugs 86 and 81. Bearing balls 9| and 92 are received in the confronting conical recesses in lugs 86, 99a and 81, 99b, whereby the bracket 99 is mounted for smooth frictionless pivotal movement about anaxis 93,

Figure 6, normal to the axis of support 65, and the axis 391). From Figures 3 and 4, it is seen that these two pivot axes are slightly offset along axis 891).

From inspection of Figures 3 and 6, it will be noted that support 65 has a bore 94 in which a headed bushing is secured by means of a nut 96. This bushing, as well as the parts connected therewith, may be duplicates of bushing H and the corresponding parts carried thereby. These have been previously described, so that it is deemed sufiicient merely to point out, sleeve 91, plunger 98 and plate 99. An upstanding lug 990 on bracket 99, has a threaded aperture in alignment with plunger 98. A contact pin I99 is adjustably threaded into this aperture for engagement with the reduced end of plunger 98. Support 65 has a pair of threaded holes I9I and I92 on opposite sides of bore 94. Parallel guide pins I93 and I94 extend loosely through respective holes in bracket 99 and threadedly engage the apertures in support 65. The outer ends of these pins carry an abutment or cap I95. A coil spring I96, which may be a duplicate of springs 89 and BI, seats in cap I95 at one end and abuts against lug 990 at its other end, thus acting to firmly urge pin I99 into contact with plunger 98. From Figure 3, it is seen that the point of contact of pin I99 and plunger 98 lies in the plane through pivot axis 93, normal to range finder axis 39b. Sleeve 91 is connected by ashaft I91 for rotation by knob 58. Since this shaft, except for length, and its connection with sleeve 91 at one end, and knob 53 at the other, may be duplicates of shaft 82 and its connections, previously described, it is deemed unneccessary to repeat the description. When knob 51 is actuated to tilt support 65, as aforesaid, bushing 95, sleeve 91, etc., pivot as a unit therewith about the axis of pins 63 and 64. Thus, the separation of sleeve 91 from knob 58 is varied. The headed ends of shaft I91, such as I98, Figure 3, and its pin I99 in the slot of sleeve II9 attached to knob 58, permit the necessary relative movement between sleeve 91 and knob 58 while permitting the sleeve to be adjusted at all times without regard to the adjustment of knob 51: Bushing 95 and sleeve 91, on the one hand, and sleeve 91 and plunger 98, on the other, have screw threads of differential pitch so that a very fine adjustment is provided.

Thus, actuation of knob 51 pivots reflector 48 about an axis parallel with the line of sight while knob 58 operates to pivot the reflector about a second axis normal to the line of sight and the range finder axis. The adjustments are at all times entirely independent.

The bracket 99 is, of course, entirely open except for supporting and abutment rim portions along its bottom and one side edge, as indicated at 99d, Figure 4. A spring clip I I I is attached to the rim 99d and presses the reflector firmly into contact with a supporting protuberance II9. At the other side of the frame, a spring clip I I2 acts to urge the reflector into contact with a pair of adjusting screws I I3 only one of which is shown. These screws are spaced in the direction of extent of rim 99d and enable a very fine adjustment of the reflector relatively to its frame- A resilient clip I I4 is mounted on the top of brack et 9.0 and engages the top edge of reflector 48,

to urge its lower edge onto its seat on the lower rim of the bracket.

The alternative mounting of the partial reflector In Figures '7, 8 and 9, I have shown an alternative mounting for'partial reflector 45" corresponding to48, Figure 4. In these figures, a ring gear I i has teeth formed upon its inner and'outer peripheries. Three radial arms H6 have'their outer ends secured to gear II5. The hub I IIa of an arcuate flanged track I H, is fixed to the inner ends of arms IIS with its axis in alignment with the axis of gear II5. Track II? defines an arcuate path about an axis normal to and concurrent with, the axis of gear H5. Hub I IIa is journaled in a portion of the range finder frame I I8, Figure 9, and the gear, hub and track are rotated by a worm H9 fixed to the end of a shaft I 28. This shaft is connected for operation by a knob 53 corresponding in all respects with knob 58, Figure 3. knob 58 adjusts the reflector 48 about an axis normal both to axis 3% and to line of sight 65.

An arcuate slide I2I is shaped to fit track I ll with a smooth and accurate fit and carries arms I22 and I23 mounting a frame 124 for reflector 48, at their adjacent ends. Suitable means, not shown, are provided to maintain slide I2I in its guide track. The dimensions are such that the central axis about which slide I2I moves, passes approximately through the center of reflector 48. The plane of the mirror lies on the axis of shaft I26, and at 45 to the common axis of curvature of track I I! and slide I2I. Slide I2I is slotted as shown, one side edge of the slot being provided with teeth I25. A stub shaft I26 is journaled in and by hub Illa and at its upper end has fixed thereto a pinion I2! meshing with teeth I25. The sun gear I28 of a differential is fixed to the lower end of shaft I26.

A ring having worm teeth I29 is mounted beneath and concentric with ring gear II5, by means of a'ball thrust bearing I30. The upper face of gear I29 has pivotally mounted thereon one or more pairs of intermeshing planetary pinions, three pairs being shown and identified by the numerals I 3|, I32 and I33. One pinion of each pair is in mesh with the internal teeth of ring gear H5 and the other of each pair is in mesh with sun gear I28. A worm 134 is fixed to shaft I35 and meshes with gear I29. Shaft I35 extends to the outside of the range finder casing where it carries a knob 5'5 corresponding in purpose and function to knob 57 Figure 3. Thus, as knob 51' is turned, gear H5 being assumed to be fixed, a drive takes place by way of Worm I34, gear I29, planetary pinions I I, I32 and I33 and gear 528, shaft i226. pinion l2? and rack I25 to shift slide I 2! relatively to track I I7.

When knob 58 is turned, to rotate track Ill about the axis of shaft I25, shaft I35 being stationary, slide I2! would be erroneously shifted in the absence of the aforementioned differential because the slide walks around the then stationary pinion I27. With the differential constructed and connected as shown, rotation of shaft I22, shaft I 35 being stationary, rotates track II? in the manner previously described, and also drives sun gear 528. by way of pinion pairs I3I, I32 and I33, to drive pinion I27 inthe direction and amount necessaryto maintain slide I2I motionless with respect to track H'i. Thus That is, rotation of the adjustments of the reflector 48 are about two mutually normal, concurrent axes while the two adjustments are entirely independent of each other, as in the species of Figures 3 to 6,

inclusive.

Geometrical optics of the range finder Rays from the target T, Figure 2, are totally reflected by entrance reflector 3| along the axis of casing 38 to, and through, partial reflector 48, and objective I34, to erecting prism I35. Thence the lines emerge downwardly and are reflected again parallel with the axis of the casing by prism I36 through reticle 45 and eyepiece lenses 56, 54 and 55, previously described. The ranging telescope thu provided is preferably 8-power with an 8-degree field of. view. From Figure 4 or 5, it will be noted that the objective holder I38 has a flange I39 secured by screws I40 within an opening in frame 42. The holder projects axially through an opening MI in support 65 so that the objective I34 lies in the plane transversely of the casing 30 through the axis defined by screws 63 and, 64. It will also be noted from Figures 4 and 5, that prisms I35- and I35 are mounted on a projection 49a of frame 49,, being clamped to the side of said projection by a plate I50, screws I5I and adjusting screws I52, threaded through plate I50. 1

Rays from the target T also enter opening 300 and fall on reflector 48. A portion of these rays are reflected through objective I34 to eyepiece 52, along the path just described and in superposed relation with the. rays proceeding from reflector 3|, and, of course, when the instrument is properly adjusted for range, the two images are exactly superposed. The manner in which the instrument is adjusted will be described under Operation.

The remainder of the rays falling on reflector 48, pass directly therethrough to and through objective I42, thence through erector I43, shown as a conventional Porro prism system, to eyelens I44 and I45. The eyepiece for these lens is carried on the rear side of the finder casing, as identified at [46, Figures 1 and 10. Thus, the tracer observer or spotter at eyepiece I46, sees two crossed images of the tracer path forming a shallow curved X. The crossover or apparent intersection of the two images is the point at which the tracer passes through the range for which the range finder is set, as will be more fully described under Operation. The spotting telescope thus provided-is preferably six power with an 8-degree field of view covering the same field as the range finder proper. This field of view includes reticle circles with I-, 2-, 3-, and 4- degree diameters concentric with the center of the field, as shown at I53, Figure 24.

A lamp I 47, Figure 2, is positioned beneath range disc 42 and, when. illuminated, causes an image of range line 43 and the range scale there adjacent, to be projected onto a small prism I48, Figure 5, secured tothe under side of prism 36. Thence the rays enter pentaprism I35 and are reflected through obiective I34 and reflector 48 to reflector 33 carried by entrance reflector 3I.- The rays are then reflected back along the axis of casing 30 and reverted on passing through doveprism I49 carried by bracket 30 and moving as a unitnwith refle'ctor'48'.

fined by reticle'mask 45a formed at one side on when the cam 38 is turned. The radius to line The" rays then pass to eyepiece 52' through the small area de'" The altitude converter On many target courses, the altitude remains substantially constant while, at the same time,

slant range changes continuously. I take advantage of this fact to simplify the adjustments of the instrument by providing mechanism whereby the range finder operator sets in adjustments for altitude which are automatically converted to slant range. From the simple trigonometry involved, it is obvious that where 60 is the angle of elevation above horizontal of the line of sight to the target, H0 is the altitude, and Do is the slant range. This may be written which is the form in which the converter, now to be described, solves the equation.

Referring to Figure 17, it will be noted that sight shaft 1 has a gear segment I56 clamped thereon and in mesh with a pinion I51 fixed to the shaft I58 of elevation or so potentiometer I59. The winding of this potentiometer is tapered sinusoidally so that its slider I60,- while rotated in accordance with the angle of elevation so of the lines of sight, produces a voltage output proportional to sin 60. The actual circuits involving this potentiometer will be subsequently described in detail. Suffice it to say for the present that the circuit connections between this potentiometer and the converter parts carried by the range finder, are effected by leads carried in a cable I6I, Figure 1, and having a conventional plug and receptacle at its ends. A cover I65 is secured to a base I64 to protect the parts carried thereby. This cover is removed in Figure 10.

The shaft M has been previously described as having disc 42 and range cam 38 fixed thereon. As shown in Figure 11, this shaft is directly connected with a coupling rod assembly I66 which extends upwardly through a protecting tube I61, Figure 1, through base I64, to the converter, where it is connected to shaft I68 of slant range potentiometer I69. Referring to Figures 10 and 12, shaft I68 has a reduced upper end to which a dielectric collar I10 is fixedj This collar has sliders HI and I12 fixed to its upper and lower faces and which make contact, respectively, with inner and outer windings I13 and I 14. As will be subsequently explained in detail, the outer winding I14 is the only one used in the converter circuit, the inner winding being used to transmit slant range electrically to the range servo in the director. The windlngs are wound upon dielectric forms secured respectively to the inner and outer surfaces of the core I15 integral with a base H501 and having a central bearing sleeve I151). The core is mount-' ed on plate or base I64, by supports I16.

A small reversible shaded pole motor I11 of about .003 H. P. is connected to drive as a 11 disc 42 and cam 38.

the shaft I68 of potentiometer I69, the range noted that this reduction drive includes a pinion I18 on the shaft of motor I11, and meshing with a gear I19 fixed to a jack shaft journaledin a frame I of the converter. A pinion I8I is fixed to the same shaft and drives a gear I82. This gear I82 is fixed upon a shaft I83 journaled in a bracket I84 bolted to frame I80. A pinion I85 is also fixed on shaft I83, between parallel, rearwardly-extending arms on bracket I84 and forming bearing supports for said shaft. Pinion I85 meshes with gear I86 formed as a unit with a bevel pinion I81, the two being fixed to a shaft I88, Figure 12. This shaft is journaled in a block I89 attached to frame I80. Pinion. I81 drives pinion I 90 fixed to shaft I9 I. This shaft is journaled in upright position by arms forming parts of block I69. A gear I92 is mounted between the aforesaid arms and is pinned to shaft I9I.

Gear I92 meshes with a gear I93 forming one element of a slip friction coupling with shaft I68. Gear I93 is journaled on a hub I94 having a circular flange adapted to be received in a central depression on the under side of gear I93. This hub is connected with shaft I68 by a pin and slot arrangement indicated at I95. Three equally circumferentially spaced screws I96 project from the lower face of gear I93. A pressure plate I91 has apertures receiving screws I96 and coil springs I98 are mounted on each screw to exert a thrust between the head thereof and plate I91. Gear I93 being axially shiftable on hub I94, the flange of said hub is clamped between the gear and plate I91. The flange is faced with friction material so that shaft I68 and sliders HI and I12, move as a unit with gear I93 under ordinary conditions. However, when the shaft I68 reaches the limits of its travel this slip connection prevents excessive torque from being exerted on the shaft by motor I11 and the inertia of the gears and other rotating parts.

As shown at Figure 10 and in detail at Figure 18, the motor I11 is provided with a flywheel I99 journaled upon motor shaft I11a. A spider 200 having a friction facing 200a, is pinned to shaft I11a on one side of the web of flywheel I99. A collar 20I is secured by set screw 202 to the end of the motor shaft. This collar has a reduced hub, splined to receive the splined opening of a second spider 203 which also has a friction facing. A coil spring 204 surrounds the hub portions of .collar 2!" and exerts a thrust urging spider 203 toward spider 200 to thereby clamp the flywheel web therebetween. As a result of this construction, there is a time lag between any change in rate or direction of rotation of the motor armature and flywheel I99 so that hunting is reduced and a smoother operation afforded. This is important because, as will subsequently appear, motor I11 may reverse rapidly in ordinary operation.

Base I64 carries a standard 205 on which are fixed three variable resistors 206, 281 and 208.. These variable resistors have slides which are settable to vary the effective resistances thereof. Each is connected in the circuits as will be subsequently explained, so that the change in volts, per yard change in slant range, corresponds with the change in volts, per yard change of altitude. The connections to these resistors will be explained in the description of the electrical circuits.

It has been explained previously, that the range From Figure 10, it will be finder does not set slant range directly but rather, sets altitude, the latter value changing less rapid- 1y than slant range under ordinary conditions of tracking. Referring to Figures 1 and 13, there is abox or casing 209 attached to the lower portion of the rear wall of director casing 5. An altitude potentiometer knob 2I0 is fixed to a shaft journaled in the right wall of this casing and. has a pinion 21 l on. its inner end. Pinion 2| 1' meshes with a gear 2I2 fixed to the shaft 2l3 of altitude potentiometer 2I4 having a slider 2l5.. This potentiometer also appears in the wiring diagrams of Figures 19 and 21 and its electrical connections will be subsequently described. Suffice it to say for the present that the range finder operator, in looking into ocular 52, adjusts knob 210 and thereby unbalances a circuit which causes motor I11 to run in one direction or the other to thereby rotate cam 38 and pivot deflector 3 I. Adjust.- ment is. thereby effected to bringv the two target images into coincidence. Whereupon, provided knobs 51 and 58 have been properly set, the range of. the. target may be read within mask 45 opposite an indicium at 41. The outer face of gear 2l2 bears. an altitude scale visible through a window 2 I 6. inthe end of casing 209, and readable against a fixed index (see Fig. 1). Switches 2I6 and 2H are mounted conveniently to knob 2I0, to control the range finder and director circuits, re.- spectively. A knob 2.18. is positioned between the switches and is turnable to adjust the intensity of light emitted by lamp. I41.

The range servo mechanism The manner in which the range is determined, by turning knob 2l0 until motor I11 rotates cam 38 to bring the two target images into coincidence, has been explained. As motor I11 rotates to drive shaft I58, both sliders HI and I12 of slant range potentiometer I69, are rotated in accordance with slant range. Outer winding I14 is used to develop a potential balancing the alti tude converter circuit. Inside winding I13 is used to develop a potential, also proportional to slant range, for controlling. the range servo mechanism which operates automatically to introduce slant range into the director.

The voltage set up by winding I13 is matched against a voltage proportional to the reading of the range. dial of the director and any difference is used to control a servo-motor which automatically changes the range setting of the director, as well as. the time. of flight set into the computer.

The range. servo potentiometer is identified at 2I9, Figures 13., 16 and 19 and includes a. winding 220v mounted upon a base 222 and having a slider 22I securedto shaft 223. Shaft 2.23 is connected by a reduction drive, generally indicated by the numerals 224, for operation by range servomotor 225 which may be a capacitor start and run machine. Referring more particularly to Figure 16, this drive includes a pinion 226 on the shaft of motor 225 and meshing with a gear 221 fixed to countershaft 228 journaled in base 222. This shaft carries apinion 229 driving a gear 230. fixed with gear 23I on second countershaft 232. Gear 23l drives a gear 233' attached to the potentiometer shaft. Gear 230 also meshes with a gear 234 fixed on range setting. shaft 235. This is the shaft on which range. handwheel I8, Figure 1, is mounted. This handwheel is. removed when the coupled range finder and its, controls are. in operation. However. the handwheel may be used, when desired, tov set in. range, exactly as. in. the. MA1, M5 or M6 directors, merely by opening the director range switch2 I1, Figures. 1 and 21. Motor 225 has a flywheel 23.6. which may be frictioncoupled with the motor shaft asv previously described for motor I11, in connection with Figure 18.

Referring to Figure 19, it. will be noted that the inside winding I13 of slant range potentiometer I69, has a second potentiometer 231 so connected that adjustment thereof changes the voltage across both the inside winding I13. of the slant range potentiometer and the range servo potentiometer 2 I 9. This potentiometer 231 is shown at Figures 13 and 14, asv mounted in. the left end of box. 209. A U-shaped bracket 238 is secured to the base 209a of box 209 and has a plate 239 secured inwardly of, parallel to and spaced from, its central or bight portion, as. by means of spacers 240 and screws 24 I. A gear 242 is journaled in the space between plate 239 and bracket 230 and has secured thereto the cylindrical support 243 of potentiometer 231, as by means of screws 244. The core and winding of thepotentiometer are secured on and externally of the support, as shown. The support has a central bearing 243a in which shaft 245 has a smooth fit. The slider 245 is secured to the inner end of shaft 245. A shaft 241 is journaled in aligned bearing apertures in plate 239 and the front wall of casing 209. This shaft carries a pinion 248 in mesh with gear 242. The end of the shaft projects. to the exterior of box 209 where it carries a trial fire knob 249. In this manner, as the knob is rotated, gear 242 and the winding of the potentiometer are turned relatively to slider 246. This is intended only to introduce adjustments based upon trial shots.

A shaft 250 has one end co-unterbored to receive the projecting end of potentiometer shaft 245, the two being secured together by a set screw 25 I. The outer end of shaft 250 has an upstanding lever 254 secured in a diametrical slot in the shaft. This lever, as well as knob 249 are located conveniently to the left hand of the tracer observer as he looks into eyepiece I46. The vertical face of bracket 238 has a circular flange 238a outstanding therefrom, concentric of shaft 245. A radially inwardly projecting lug 23% forms a fixed abutment for a coil spring. 252 located in the chamber formed by flange 238a and the inner coaxial end of. shaft 250. This shaft has a lug 259a normally held in radial. alignment with lug 2381), by spring 252. The spring is held in place by a circular flange 25011 fitting within flange 238a. Thus, lever 254 may be pivoted in one direction or the other. against the action of spring 252, to move slider 245 over the winding of. potentiometer 231. When the lever. is released, the compressed spring acts. to restore it to initial or center. position in which the lugs 238D and 250a are in precise alignment.

From the hook-upv of. the potentiometer windings I13, 220 and 231, as disclosed in Figure 19, it will be apparent that the potentials. across I13 and 21 9 are in opposition. and that any difference is applied. to anv input. of. amplifier 2.55, subsequently described in detail. The range adjustment potentiometer 231, is effective to change. the voltage across both the windings I13 and 220. This correspondingly changes. the ratio of volts per yard, e. g., the calibration of. the. instrument and causes range servomotor. 22.5 to change. the range being set into the. director so that it no longer coincides with the setting of the. range finder. Hence the. tracer observer may operate handle 25.4. in accordance. with. the observed crossover with respect to the target, of the two images of the tracer path in his field of view, to thereby increase or decrease the range setting of the director with respect to that being introduced by the range finder.

Under conditions wherein slider 246 is stationary, and the sliders I12 and 22I are at equal potential points on potentiometers I13 and 226 there is no input to amplifier 255, and motor 225 is at rest. When the voltages are unequal, the input to amplifier 255, will depend in phase upon the predominating voltage and in amplitude upon the voltage difference. The resulting amplified output causes motor 225 to turn in the direction necessary to so move slider 22I as to balance the voltage from line 261a to slider 22I with the voltage from line 261a to slider I12. As a result, motor 225 is turned proportionally to the range setting of the range finder, and its rotation may be used to set range into the director by way of gear 234 and shaft 235, in the manner previously described.

The electrical circuits Figure 19 shows a simplified wiring diagram of the combined altitude converter and range,

servo circuits. Taking up first the altitude converter circuits, leads 256 and 251 including variable resistors 268 and 266, respectively, extend from the terminals 214 and 261 of a 115-volt, (SO-cycle supply, to the corresponding terminals of outer winding I14 of the slant range potentiometer. Variable resistors 266 and 268 may have a rating of 10 watts and total resistances of 250 and 100 ohms, respectively. Corresponding leads 258 and 259, extend from the source to the terminals of the winding of altitude potentiometer 2M. Lead 258 includes a variable resistor 266 of 10 watts and 500 ohms. Likewise, one terminal of the aforesaid source, is directly connected by lead 26I to a terminal of the winding of sin 60 potentiometer I59, the other terminal of I59 being connected over lead 262 to the slider I1I of winding I14. ometers I59 and 2 I4, are connected by respective lead 263 and 264, to the input of one section of amplifier 255. By the connections shown, the voltage from slant range winding I14 is impressed on sin 60 potentiometer I59 so that a voltage proportional to D sin 60 is obtained. As shown, this voltage is connected in series with the voltage from altitude potentiometer 2 I4, the connections being made so that one voltage is subtracted from the other and any difference fed to the corresponding section of amplifier 255 having its output connected by leads 265 and 266 to control motor I11. The phase of the voltage fed to amplifier 255 will depend upon the predominating one of the algebraically added voltages and the motor I11 will rotate in a direction depending upon the phase of the amplified algebraic sum. Thus, when altitude slider 2I5 is manually adjusted by knob 2I6, the previously balanced circuit is unbalanced and a net voltage is fed to amplifier 255 whose phase will depend upon the direction in which the slider is adjusted and whose amplitude will depend upon the amount of adjustment of the slider. rotate and, through the previously-described speed-reducing drive, rotate slider I1I in the direction necessary to again balance the opposed voltages. At the same time motor I11 rotates cam 38 of the range finder and pivots entrance reflector 3|.

The range finder operator, then, while looking into eyepiece 52, adjusts knob 2| 0 and, in so The sliders I60 and 2I5 of potenti- Motor 111 will then" doing, causes the operation of motor I11 in the direction and amount necessary to bring into coincidence the two images of the target as refiected from respective reflectors 3I and 48. When coincidence has been effected, the range may be read within reticle mask 45a and, by the range servo mechanism, is introduced into the director. It will be noted that the range finder operator does not directly set range, but altitude, which may be read at window 2I6', Figure 1. Since, for many target courses, altitude changes but slowly, while at the same time, range may be changing rapidly, the invention gives the operator a much more precise and sensitive con trol than would be the case were he requiredto set range directly. Furthermore, he is enabled to effect range adjustments more rapidly and is enabled, with relative ease, to maintain the range finder properly adjusted for rapid changes of range.

By the construction previously described in connection with Figure 10, motor I11 operates to adjust slider I12 of inside winding I13 of the slant range potentiometer, the drive being indicated by dotted line I68, Figure 19. One lead 261a of a volt, 60-cycle source, connects through resistor 201, with one terminal of winding I13. The remaining terminal is connected by lead 268, through variable resistor 269 of 10 watts and ohms, with one terminal of the Winding of range adjustment potentiometer 231. The slider I12 of winding I13 is connected by a lead 210 with one input terminal of a second section of amplifier 255. Lead 2610. is also connected, through a variable resistor 21I' of 10 watts and 100 ohms, with one terminal of the winding 220 of range servo potentiometer 2I9. The two remaining terminals of windings 220 and 231, are directly connected by a lead 21I. The slider 22I of range servo potentiometer 2l9, is connected by a lead 212 to the other input terminal of the second section of the amplifier. The slider 246 of range adjustment potentiometer 231 is connected through variable resistor 213 of 10 watts and 300 ohms and a, lead 2140., with the remaining terminal of the current supply. Actually, as will appear from Figures 21 and 22, all current supply is from one and the same source, the connections having been omitted in Figure 19 to avoid confusion. This fact is indicated by the use of the reference characters 261, 21 4, 261a, 214a, etc., upon Figure 19.

From the hook-up disclosed, it will be clear that range adjustment potentiometer is so connected that varying it changes the voltage across both the winding I13 of slant range potentiometer I69, and winding 226 of range servo potentiometer 2I9. It will also be clear that the voltage from line 251a to slider 22I is matched or balanced against that from line 26111 to slider I12 so that any difference between the two, is fed to the input of the second section of amplifier 255 over leads 210 and 212 and, after amplification, applied to motor 225 to cause the same to operate in a direction and at a speed depending, respectively, upon the phase and amplitude of the resultant voltage. The manner in which the amplifier operates will be subsequently de scribed. Motor 225, being connected to slider 22E by way of drive 224, previously described, adjusts potentiometer 2I9 to balance the two voltages and bring their difference to zero. At the same time, as previously described, motor 225 acts to introduce range into the director. The range so set is continuously indicated by. dial I9,

17 "The parts areso arranged thatthe range "spotter, looking into "eyepiece I46; has lever 254"convenient tUhislefthand. It will'be recalledthat this lever is connected "to adjust "slider" 245 of the rangaadjustmentpotentiometer. Suchadjustment imbalances the circuit so" thatmotor" 225 I mustrun in a direction depending upon the directionof adjustment 'ofsliderflfi', tomove slider 22] to a newpositi'on for balanced voltages. "As a result, a range is' set' intothe'director'which is greater or-less than that determined bythe range finder. The correction, of'course, is based "upon the spottersobservations-of thetracer crossovers with respect to the target. One lead' 2'6'lb ex-tends from-the source of-A'j Cxto a-center'tap on motor 225' while the remaining lead ZMb-from said-source, extends tooneof three outputter- *minals of the secondsectionof amplifier 255. The remainingtwo terminals -of-motor-' 225 are connected by leads 215 and 216 with the two remainingoutput terminals "of thesecond section -of-the am-pli-fier. The action is-smooth,' continuousand withoutappreciable time-lag. Hunt- 'ing-ofmotors l'17 and-255-is reduced to a-minimum so that-adelicate and substantially instantaneous response is-obtained to manual adjustments ofsliders 2I5-and- 246. The range'thus -iIlt1OdllOd-illtU-th8 director isthat determined by the range finder; plus'or" minus -any corrections effected by slider- 246; The field coils "of JllOtOl l'l'l' are supplied from leads 2370 and 2140. 'Figure -21 sh-o-ws the-circuit connections' for thetparts carried Within box 209. A terminal block 2", indicated in dotted lines upon this-figure, is mount'ed within the director casing. "The ;:termina'lsoff-this b ock are identified by capital letters. Each terminal is connected with its cor- =.respondi-ngly identified pole of a'-1-2-pole plug schematicallyidentifiedat 218; whichis adapted :to be connected by a 12-wire cable having re- "ceptacles at its ends;'with a-plug on-the-ampliiier and schematically shown at 219; Figure 22. The bundle of leads from the'variouscon-necltions'iin b'ox 20S, p'ass to the -ampli-fier indirector casing 5, through-cableconnector 28U;"-Figure l3. :From terminal-block 211;Figur'21,-'appropriate ilea'ds extend to' a 9-'pole"reeeptacle --f-63ce;adapted Jto receive plug H53 (see Figure 1) Referringto Figure 20,thei variousleadsfrom the parts oft-he altitudelconverter disposed' on base I 64 I on "range finder 21; are carried through fitting 162a and flexible cablei-l 6 I- :to p1ug ii 163: in a conventional manner. ifFors ease of understanding-, the various poles leading to receptacle I63a,*'Figure 21;and from plug I63, FigureVZO, have been given the same, lower-case letters as have been used to identify :the corresponding poles onblocli: 2.1.1. and plug 218. Since-thesame reference characters have been "used wupon' Figure21 as were fused :to identify corresponding "parts i'on'Figure 19,1'itx1s deemed sufiicient merely' to describe those parts .on' Figure' 21 which do notxappeariinlFigurei19. Referring-itocFigure 21 and masterterminal blocklll, it will be.uric'.erstood from previous (description that i p'oles A and B, are connected with the s'ource of A. C. supply. Pole'Cis connected by' lead 28 I with one terminal of range *18 or and: the intensity'ofillumination of range scale disc 42;may'be' varied to -'suit'the conditions ofambient light. A; C. currentissupplied'to the'altitudeconverter" from'pole A and"1ead261, "to one terminalof rangefinder switch "21 6 "(see "Figure 1 also) thence over lead "2610 'to pole. f, 'r'eturn-beingfby way or pole" b' and lead 2140110 poleB. Pole Gc'onnects'one input of the-second section' of theamplifienxwith" "slider- I 1 z-"of' slant rangdpotentiometer, byway ofiead' 210. 'Pole connects the "other input "terminal of--said "amplifier'section; byway of'lead' 212*,with slider '221' pfpotentiometeril9. Poles J and'K are connectedby leads285 and 266','respectively;be- "tween theoutputterminalsof the'first section "Of'..'2inip1ifier"255' "andthe poles of motor" ITI. Poles L 'and' M areronnected' over leads 215' and 21 6;"ib'etWB'6ntWOU1ltDllll terminals of the second section of amplifier 2 5 5 and two terminals "'of range servo motor 2 2 5. "'"The' third motor termina1is connected" bylead "26'ib through "director range switch "2 l l; and" rangefinden'switch 21 6, to A. Ctsupplyat-pole A. Thus'both" switches mustbe "closedforenergization of" motor 225135 "288a? Figure 20 "extends from *one terminal" of 'insidewinding H 3 of slantrange "potentiometer "IGQJby Way ofpoles lead268, resistor 269 to'potentiometer' 2'31. A"1e'ad2'62a; extends from the *slidenl l I, by "Wayof poles "p; "1ead262 and pole P to one terminal ofthe winding 'ofpotentiorneter" I59 Since bothpotentiometer ['59 and amplifier '255are positioned within the director c'asing no'pole' is providedio'r lead 263 between slider 13 Uandtheamplifier. inputjithe connection beingimadedirectly. Stillreferring tdFigur 20, the two" terminals of winding I M; aredirectly connected by lead256 andresistor' ntl, andiby lead 25'! and resistor 206, totheterminals of motor'i1'i,"'which are "connected to *the"'A'.' C. source from poles A and B.

Theo amplifier Amplifier 255 is provided to supply sufiicient power to operatethe motors under controlnof thesmallvpotential' differences created as va resultof unbalance in the circuits, previously mentioned. 'i'Ihe two. sections of this amplifier have been previously. mentionedand, in effect; the. two sections are separate. and distinct, one. being controlled by unbalanc'ed potentials in the altit'ude converter circuit and,'in turn controlling motor'l 11,' the other. being controlled by. potential"differenceslini'the range servoi'and, inlturn controlling rnotoiT 225.

"Referring to Figure" 2-2; the 1 12-p'o1el plu of the amplifier, .has previously been described.

' 'Correspontiing' lettered poles of 'these plugs are scale light rheostat 2l8a, whose oper'ating'knob connected b-y12-wire cable having receptacles at its ends. Of these the Wires connected between poles A and'B are tapp'edtolthe'A. 'C. supply at the director terminal block. v Also the wire 7 connecting poles A is tapped to one winding terminal ofsine e0 potentiometer I59, to m'akeo thedirect connection shown at Figure 19. "The wire'ofrthe :iafore'said cable, "not shown, connecting. 'poles P is 'cut' intermediate. itsiends, 'to form two terminals "One" terminal is connected to" the remain- ;ing terminal of"potentiom'eter I59 and the" other -to theslider 1'60, thereof.

Referring to block 219, Figure 22, a lead.261d connects pole A" with" the. primary i of" a "transformer 285, return beingithrough 'ilead'. 214d; to

"pole B; One "secondary" winding 285a :supplies filament current to the' tubes and also supplies 

